# Automorphism Group of C Over R

## Theorem

The field extension $\C / \R$ of complex numbers $\C$ over real numbers $\R$ has automorphism group $\operatorname{Aut}$:

- $\operatorname{Aut} \paren {\C / \R} = \set {\operatorname{id}, \sigma}$

where:

- $\operatorname{id}$ denotes the identity mapping
- $\sigma$ denotes complex conjugation